Vistek Imaging and Photographic Terminology Database

r

Random Access Memory. The high speed portion of the computer's memory that is held on special chips.

Rangefinder

A device included on many cameras as an aid in focusing. See also Viewfinder, Parralax Error

Raster

The series of lines of information such as the parallel and horizontal scan lines that form a television or video display image.

Raster image

This is a resolution - dependant image that is produced using pixels. The quality of a low - resolution image decreases as you zoom in to the image. Photoshop is raster software.

Raster Scan

A scanning pattern, generally from left to right while progressing from top to bottom of the imaging sensor or the display monitor. Generally comprised of two fields composed of odd and even lines.

Rasterization

Converting mathematical and digital information into a series of dots by an imagesetter for the production of negative or positive film.

Raw data

Data that is not formatted or processed.

RAW image format

The most common image format amongst digital cameras is JPEG, it's a format which produces relatively small files from large amounts of image data by discarding certain information, as JPEG uses a "lossy compression algorithm". The only other common alternative is TIFF, this produces an uncompressed 24-bit per pixel image often in the multiple megabytes, certainly for a 3 megapixel camera in excess of 8 MB per image, not really practical. Each pixel of a CCD can only see one colour, depending on the CFA (colour filter array) placed over the CCD this is either Red/Green/Blue or Cyan/Magenta/Green/Yellow. The cameras internal image processing engine then interpolates colours from the value of neighboring pixels to calculate a full 24-bit colour for each pixel. RAW is simply the raw data as it comes directly off the CCD, no in-camera processing is performed. Typically this data is 8, 10 or 12 bits per pixel. The advantage being that file sizes are considerably smaller (e.g. 2160 x 1440 x 12 bits = 37,324,800 bits = 4,665,600 bytes), the image has not been processed or white balanced which means you can correct the image, and it's a better representation of the "digital negative" captured. The disadvantage is you can't open these image files with a normal photo package without using an "acquire module" (a plug-in, typically TWAIN, which can open / process such images). Advantages of RAW format A true "digital negative", untouched by cameras processing algorithms No sharpening applied No gamma or level correction applied No white balance applied No colour correction applied Lossless yet considerably smaller than TIFF Records data over a wider bit range (typically 10 or 12 bits) than JPEG or 8-bit TIFF Disadvantages of RAW format Requires proprietary acquire module (typically TWAIN) or plug-in to open images Images can take 20-40 seconds to process on an average machine No universally accepted RAW standard format, each manufacturer (even each camera) differs.

Reboot

The process of turning a computer system or printer off and then back on again, to reload the software.

Reciprocity failure

Films are designed to be exposed within a limited but practical brightness range. Reciprocity failure occurs when a film is exposed under conditions that are not within its design range. It usually becomes evident with very low shutter speeds, such as those used in dim night scenes. As a result of reciprocity failure, colour balance will shift and colours will seem less natural looking.

Reciprocity law

States that exposure = intensity x times, where intensity is equal to the amount of light and time is equal to the time that amount of light is allowed to act upon the photographic emulsion.

Recycling time

Is the time it takes a flash unit to recharge between firings.

Red eye

The appearance of deep red dots in the eyes of human and animal photographic subjects. Redeye is is caused by the flash reflecting off the retina in their eyes. It can be prevented by adjusting the camera angle, being sure the subject does not look straight at the flash, or with a redeye-reducing pre-flash. The pre-flash causes the subjects' pupils to contract, reducing the visible retina and thus the possibility of light reflecting from it.

Red-eye Reduction Mode

A special flash mode whereby a pre-flash or a series of low-powered flashes are emitted before the main flash goes off to expose the picture. This causes the pupil in the human eye to close and helps eliminate red-eye.

Reducers

Are solution which removes silver from negatives and prints. They are used to diminish density and alter contrast on a photographic emulsion.

Reducing agent

Is a chemical in a developing solution which converts exposed silver halides to black metallic silver.

Reflected light reading

Is a measurement by a light meter of the amount of reflected light being bounced off the subject. The light meter is pointed towards the subject.

Reflections

Are rays of light which strikes a surface and bounce back again. Specular reflection occurs on even, polished surfaces; diffuse reflection occurs on uneven surfaces, when light scatters.

Reflector

Any material or surface that reflects light. Reflectors are often used in photography to soften the effect of the main light or to bounce illumination into subjects shadows.

Reflex

A reflex camera is one that utilizes a mirror system to reflect the light, and therefore the image, coming through the lens, to a visible screen. The image seen in the cameras viewfinder then is the same image entering the lens. This system provides the most accurate framing and focusing. Most reflex cameras reveal a high percentage of the image that will be photographed, upwards of 80%. Some reflex cameras are able to show 100% of the image frame into the viewfinder. The reflex system avoids the parallax problem that plagues most direct view cameras.

Refractive index

Is a numerical value indicating the light bending power of a medium such as glass. The greater the bending power, the greater the refractive index.

Refractive index

Is a numerical value indicating the light bending power of a medium such as glass. The greater the bending power, the greater the refractive index.

Refresh rate

The rate at which an image is redrawn on a CRT. This is needed because the phosphors at each pixel are stimulated by the electron gun for only a brief time. The faster the refresh rate, the more stable an image will appear on the screen.

Registration marks

Small crosshair on film used to align individual layers of film negatives.

Replenisher

A substance added to some types of developers after use to replace exhausted chemicals so that the developer can be used again.

Resample

To change the resolution of an image. Resolution: Refers to the sharpness and clarity of an image. The term is most often used to describe monitors, printers, and bit-mapped graphic images. In the case of dot-matrix and laser printers, the resolution indicates the number of dots per inch. For example, a 300-dpi (dots per inch) printer is one that is capable of printing 300 distinct dots in a line 1 inch long. This means it can print 90,000 dots per square inch. For graphics monitors, the screen resolution signifies the number of dots (pixels) on the entire screen. For example, a 640-by-480 pixel screen is capable of displaying 640 distinct dots on each of 480 lines, or about 300,000 pixels. This translates into different dpi measurements depending on the size of the screen. For example, a 15-inch VGA monitor (640x480) displays about 50 dots per inch. Printers, monitors, scanners, and other I/O devices are often classified as high resolution, medium resolution, or low resolution. The actual resolution ranges for each of these grades is constantly shifting as the technology improves.

Resolution

Refers to the sharpness and clarity of an image. The term is most often used to describe monitors, printers, and bit-mapped graphic images. In the case of dot-matrix and laser printers, the resolution indicates the number of dots per inch. For example, a 300-dpi (dots per inch) printer is one that is capable of printing 300 distinct dots in a line 1 inch long. This means it can print 90,000 dots per square inch. For graphics monitors, the screen resolution signifies the number of dots (pixels) on the entire screen. For example, a 640-by-480 pixel screen is capable of displaying 640 distinct dots on each of 480 lines, or about 300,000 pixels. This translates into different dpi measurements depending on the size of the screen. For example, a 15-inch VGA monitor (640x480) displays about 50 dots per inch. Printers, monitors, scanners, and other I/O devices are often classified as high resolution, medium resolution, or low resolution. The actual resolution ranges for each of these grades is constantly shifting as the technology improves.Standard resolution is 640 x 480 pixels (H x V) and originates with the VGA standard first defined for the IBM PC. SVGA is the next step up in terms of resolution and covers 800 x 600. XGA define the 1024 x 768 resolution, while UXGA is used for 1280x1024 and 1600x1200. The higher the resolution the finer the image detail that can be seen. Also used in measuring image size and resolution, i.e., 640 X 480 is the pixel resolution of most VGA Monitors. (Note pixels are square in computers and most digital cameras, they are rectangular in video cameras and television). The bit depth and surface size of the individual pixels on an image sensor controls its sensitivity to light. (Equivalent ISO).

Resolution, output

The number of dots per inch, dpi, used to display an image on a display device (monitor) or in print.

Resolving power

The resolving power of a lens is a measure of its ability to closely spaced objects so they are recognizable as individual objects. It is determined by photographing a series of closely spaced lines, measuring the spacing between the most closely spaced lines that appear separate on film. The resolving power is expressed as the number of lines pairs per millimeter.

Reticulation

A crinkling of the gelatin emulsion on film that can be caused by extreme changes of temperature or acidity / alkalinity during processing.

Retina

The area at the back of the human eye that converts incoming light into electrical impulses sent to the brain.

Retouching

Removing imperfection or unwanted portions of an image.

Reversal

A process for making a positive image directly from film exposed in the camera; also for making a negative image directly from a negative or a positive image from a positive transparency.

Reversal film

Film that produces a positive image (transparency) on exposure and development.

RGB

The red, green, and blue colour model used for scanners and monitors.

RIFF (Raster Image File Format)

A storage format used with gray-scale images.

Right reading

The correct orientation of a negative or transparency when the image appears as it did to the camera. Both negative and transparencies should be viewed with the emulsion side down and the base facing the observer. The emulsion side is dull-finished and very slight ridges can often be seen at the edges of the image elements. The base side appears glossy and smooth.

Rimlighting

Lighting in which the subject appears outlined against a dark background. Usually the light source is above and behind the subject, but rimlit photographs can look quite different from conventional backlit images, in which the background is usually bright.

A circular lamp or bundles of optical fibers arranged around the perimeter of an objective lens to illuminate the object in the field below it. A wide variety of sizes are available on both a stock and custom basis.

Rinse

Is a brief clean water wash between steps of a processing cycle to reduce carry-over of one solution into another.

ROM

Read Only Memory. A memory type that cannot be change or rewritten and will not lose information when a computer is turned off.

Royalty

Payment to the holder of a patent or copyright or resource for the right to use their property

Rubber stamp

This tool is used to retouch flaws, make a copy of a selected area and paste it elsewhere, or reproduce an object.

Rule of thirds

A general composition guideline that divides the negative frame into thirds horizontally and vertically to position the subject